1. Field of the Invention
The present invention is directed to a method for making multipoint connections between a plurality of terminal equipment of a data communication network according to the Standard ITU-T H.323, wherein logical channels for payload data transmission are opened up between first terminal equipment and second terminal equipment, and logical channels for payload data transmission of a consultation connection are opened up between the first terminal equipment and third terminal equipment.
2. Description of the Prior Art
Multipoint connections between a plurality of subscribers of a communication network are known as conference circuits that are controlled by a central conference circuit controller which is also provided in the communication network. For example, multipoint control units MCU contained in a communication network may be used. Given a multipoint connection upon employment of such multipoint control units, terminal devices have a respective point-to-point connection to the multipoint control unit. This multipoint control unit implements a multipoint function that also is referred to as multipoint processing. In this multipoint processing, the data streams of the individual point-to-point connections are handled such that the data streams coming from individual terminal equipment are mixed together and the respectively produced mixture is transmitted to the corresponding terminal devices. Such a procedure is described, for example, in the Standard ITU-T H.323, Clause 6.8.1 under the designation xe2x80x9cCentralized Conference.xe2x80x9d
Before a centrally controlled conference according to ITU-T H.323, 6.8.1 is initiated, all subscribers of the conference are informed of the point in time of the conference beginning. To this end, all subscribers of the conference are provided with a specific MCU address as well as the point in time at which each of the subscribers should initiate the setup of a point-to-point connection upon employment of this MCU address. As an alternative, the MCU can initiate a point-to-point connection to each of these subscribers at the communicated point in time.
A multipoint communication with decentralized control is also known wherein a multipoint control is only provided for processing a multipoint signaling. Such decentralized multipoint control can, for example, be effected in terminal equipment or in a multipoint control unit. Given such a multipoint communication, each of the participating terminal equipment sends the payload information to a multicast address prescribed by the multipoint control wherein the multipoint control assigns a plurality of different multicast addresses and informs each terminal equipment of a multicast address for its information to be transmitted. Each terminal equipment thus both transmits to a specific multicast address and receives the information sent to the other multicast addresses assigned by the multipoint control. To this end, all participating terminal equipment must support multicast functions. Alternatively to the employment of multicast, multi-unicast can be provided. In this method, the terminal equipment send the data streams to be transmitted to the other terminal equipment respectively participating in the multipoint connection upon employment of multiple point-to-point connections.
Such a procedure is described, for example, in the Standard ITU-T H.323, Clause 6.8.2, under the title xe2x80x9cDecentralized Conference.xe2x80x9d The following conditions must be met in order to establish a multipoint communication with decentralized control according to this standard proceeding from an existing call between first subscriber A and a second subscriber B:
at least one of the subscribers A and B must have a terminal equipment with multipoint control or a gate keeper that is available must have a multipoint control;
all participating terminal equipment must support multicast functionality or multi-unicast functionality.
A gate keeper is a logical function for satisfying standard functions such as address resolution or broadband administration. Address resolution means that a calling terminal point sends an alias address of a terminal point to be called to the gate keeper and receives the transport address (i.e., the Internet protocol address and the port number), from the gate keeper. The gate keeper knows the traffic volume with respect to real-time applications within the network area for which it is responsible.
Over and above this, the subscriber A or, respectively, B that initiates a consultation call to a further subscriber C during the existence of a call between the subscribers A and B must typically define, upon setup of this consultation call, subscribers A and B with a multipoint connection.
The above-described examples for setting up a centrally controlled or decentrally controlled multipoint connection setup do not, however, enable a flexible setup of a three-party conference proceeding from a two-subscriber call with consultation call.
An object of the present invention, therefore, is to specify a method for making multipoint connections between a plurality of terminal equipment of a data communication network according to the Standard ITU-T H.323 for that case wherein logical channels for payload data transmission are opened up between a first terminal equipment and a second terminal equipment, and logical channels for payload data transmission of a consultation connection are opened up between this first terminal equipment and third terminal equipment.
Accordingly, pursuant to an embodiment of the method of the present invention, such method includes the steps of: communicating a connection setup message, including a request for establishing a multipoint connection from the first terminal equipment, to a conference unit provided in the data communication network; communicating an acknowledgment message, including an identifier of a prepared multipoint connection from the conference unit, to the first terminal equipment; communicating a performance feature message for call redirection from the first terminal equipment respectively to the second and to the third terminal equipment with the call redirection destination conference unit while indicating the identifier of the prepared multipoint connection; communicating a connection setup message upon specification of the identifier of the prepared multipoint connection respectively from the second terminal equipment and third terminal equipment to the conference unit; communicating a respective acknowledgment message in response to the connection setup message to the second terminal equipment and third terminal equipment as reaction thereto; clearing down the connections existing between the terminal equipment by the second and third terminal equipment; and communicating a performance feature message respectively from the conference unit to all terminal equipment participating in the multipoint connection in order to initiate the opening of logical channels for payload data transmission between this terminal equipment via the conference unit.
A precondition for implementing this first version of the inventive method is that terminal equipment initiating a multipoint connection must maintain point-to-point connections to all other terminal equipment provided for the multipoint connection. The one terminal equipment initiates the other terminal equipment to respectively setup a connection to the conference unit and, after setup of a signaling connection to the conference unit, respectively initiates the clear down of the existing point-to-point connection to the first terminal equipment. The one terminal equipment thereby informs the other terminal equipment of a call identifier previously communicated from the conference unit.
This call identifier can, for example, be an address of the conference unit allocated to this call by the conference unit; the conference unit being indicated as call redirection destination for the other terminal equipment. The call redirection destination, however, also can be an address of the conference unit that is not permanently allocated to the call. In this case, a call identifier allocated to the multipoint connection to be setup by the conference unit is additionally communicated to the terminal equipment and is communicated to the conference unit from this given connection setup.
After a signaling connection has been respectively setup between the conference unit and the individual terminal equipment participating in the multipoint connection, and the previously existing connections between the individual terminal equipment have been cleared down, logical channels are opened up between all terminal equipment via the conference unit for payload data transmission. To this end, the conference unit communicates a performance feature message to each of the terminal equipment. A mixer for mixing the data streams coming from the individual terminal equipment is contained, for example, in the conference unit. Such a mixer preferably makes a mixture of the useful data streams coming from the other terminal equipment available to one terminal equipment.
Pursuant to a second embodiment of the method of the present invention, the aforementioned object is achieved via the following steps: communicating a connection setup message, including a request for establishing a multipoint connection upon specification of addresses of the terminal equipment to participate in this multipoint connection from the first terminal equipment, to a conference unit provided in the data communication network; communicating an acknowledgment message from the conference unit to the first terminal equipment; communicating a respective connection setup message for a multipoint connection from the conference unit to the second and third terminal equipment; communicating a performance feature message for reporting the successful signaling connection setup to all terminal equipment participating in the multipoint connection from the conference unit to the first terminal equipment; clearing down the existing connections between the first terminal equipment and the second terminal equipment as well as between the first terminal equipment and the third terminal equipment, initiated by messages output by the first terminal equipment; and communicating a performance feature message from the conference unit to all terminal equipment to participate in the multipoint connection in order to initiate the opening of logical channels for payload data transmission between the terminal equipment via the conference unit.
A pre-condition for implementing this second embodiment of the method of the inventive method is, likewise, that terminal equipment initiating a multipoint connection maintains point-to-point connections to all other terminal equipment provided for the multipoint connection. The one terminal equipment initiates the conference unit to respectively setup a connection to the other terminal equipment. After setting up a signaling connection from the conference unit to all terminal equipment provided for the multipoint connection, the conference unit initiates the one terminal equipment to clear down the connections existing between this terminal equipment and the other terminal equipment.
After a respective signaling connection has been setup between the conference unit and the individual terminal equipment to participate in the multipoint connection, and after the previously existing connections between individual terminal equipment have been cleared down, logical channels for payload data transmission between all terminal equipment are opened up via the conference unit. To this end, the conference unit communicates a corresponding performance feature message to each of the terminal equipment. A mixer for mixing the data streams coming from the individual terminal equipment is contained, for example, in the conference unit. Such a mixer preferably makes a mixture of the payload data streams coming from the other terminal equipment available to one terminal equipment.
Additional features and advantages of the present invention are described in, and will be apparent from, the Detailed Description of the Preferred Embodiments and the Drawings.